1. Field of the Invention
The present invention generally relates to a semiconductor device in which electronic components such as semiconductor chips are supported by a wiring board, and more particularly to a semiconductor device having projection electrodes such as electrodes of a ball grid array type (hereinafter simply referred to as BGA type).
Recently, the integration density of semiconductor chips has been drastically increased and it has been required to increase the mounting density of semiconductor devices.
Under the above situation, there has been considerable activity in the development of BGA type semiconductor devices, which has advantages in which electrodes (terminals) for external connections can be arranged on the back surfaces of the semiconductor devices at a relatively wide pitch and are hardly deformed. These advantages are attractive as compared to QFP type semiconductor devices. However, recently it has been required, as the integration density of the semiconductor chips has been increased and the amount of heat radiated therefrom has thus been increased, to provide BGA type semiconductor devices having a structure enabling more effective and efficient heat radiating performance.
2. Description of the Related Art
FIG. 1 is a perspective view of a conventional BGA type semiconductor device. A BGA type 10 shown in FIG. 1 is a semiconductor chip (an LSI chip) 14, which is a bare chip, a sealing part 16, and SnPb solder bumps 18 having a ball shape. Electrodes (not shown) provided on the semiconductor chip 14 and electrodes provided on the front surface of the wiring board 12 are bonded together by wires. The electrodes provided on the wiring board 12 and the solder bumps 18 provided on the back surface of the wiring board 12 are electrically connected together through wiring layers and via holes formed inside the wiring board 12. The surfaces of the semiconductor chip 14 and the wiring board 12 are sealed by the sealing part 16 made of resin. The solder bumps 18 function as terminals (electrodes) for external connections, and are arranged on the back surface of the wiring board 12 in a matrix formation. Generally, the interval T between the adjacent solder bumps 18 is equal to or less than 1.5 mm.
The BGA type semiconductor device 10 can be mounted on a mother board 20, which may be a glass-epoxy resin board. On the mother board 20, there are provided electrodes 22 arranged in a matrix formation and wiring lines. The semiconductor bumps 18 can be soldered to the electrodes 20 on the mother board 20 in a state in which the bumps 18 are in contact with the electrodes 20.
As described above, the semiconductor chip generates an increased amount of heat as the integration density thereof is increased. Hence, it is required to provide BGA type semiconductor devices having a structure that enables effective and efficient heat radiating performance.
FIG. 2 shows a conventional BGA type semiconductor device taking into account heat radiation. A BGA type semiconductor device 24 shown in FIG. 2 includes a semiconductor chip (LSI chip) 30 fastened to a recess portion of a wiring board (which may be referred to as a package or case) 26 by Ag epoxy resin adhesive 32. The wiring board 26 is made of glass epoxy resin, and includes inner wiring layers 28 having a multilayer structure. Each of the wiring layers 28 is, for example, 35 .mu.m thick. The wiring layers 28 are connected to ball-shaped solder bumps 40 through via holes (not shown). The semiconductor chip 30 and the wiring board 26 are bonded together by wires 46. The recess portion that accommodates the semiconductor chip 30 is sealed by a lid 42.
As shown in FIG. 2, thermal vias 34 are provided between the bottom surface of the recess portion of the wiring board 26 and the upper surface thereof. The inner walls of the thermal vias 34 are covered by a metallic material having a high thermal conductivity, such as copper (copper plating). A heat radiating fin 36 is fixed to the upper surface of the wiring board 26 by a silicone adhesive 38 so that the fin 36 covers the thermal vias 34.
However, the conventional BGA type semiconductor device 24 shown in FIG. 2 has a disadvantage in that heat generated by the semiconductor chip 30 can be radiated only through the heat radiating fin 36 and thus effective and efficient heat radiating performance cannot be obtained.